Two identical marbles are dropped simultaneously into separate graduated cylinders, one filled with glycerine and the other with water. The marble dropped in glycerine will quickly reach terminal velocity, obtaining a slow and constant velocity that can be measured.

Equipment

Location

ID Number

Graduated cylinder filled with water

FM, Bay A5, Shelf #1

Graduated cylinder filled with glycerin

FM, Bay A5, Shelf #1

Marbles

FM, Bay A5, Shelf #1

Important Setup Notes:

Don't spill the glycerin - it's difficult to clean up.

Setup and Procedure:

Fill non-glycerin cylinder with water so that fluid height levels in each cylinder match.

Place cylinders on table side-by-side.

Grab two marbles of identical size and weight.

Hold one marble in each hand above each cylinder.

From the same height, drop each marble at the same time, and observe the velocity differences.

Cautions, Warnings, or Safety Concerns:

N/A

Discussion:

Suppose there is a body being accelerated by two opposing forces. One of these forces is constant, and the other is velocity-dependent. There will be a point in the body's trajectory when the two forces exactly cancel, and the body is no longer accelerating. The velocity at which this occurs is called the body's terminal velocity. Such velocity-dependent forces frequently occur in fluids such as air and glycerol in the form of resistance. Glycerol is a highly viscous fluid which means it is resistant to flowing. Thus, the resistance force on the marbles quickly reaches a point when gravity is just balanced. In a less viscous fluid such as water, it takes longer to reach this point.